1. Field of the Invention
The present invention relates to a method for producing an artificial tooth, being a reproduction of the original natural tooth to be replaced or a corresponding natural tooth. It is understandably desirable that the artificial tooth to be produced as a reproduction of an original natural element should be as natural a copy as possible. The natural appearance of the original natural element or tooth should be copied therefore as closely as possible. The appearance of both the artificial tooth and the original natural element is composed from a number of properties, such as color, translucency, lightness of the colors, brightness, etc.
2. Brief Description of the Related Art
In the field of the dental profession it has longsince been established, that the more natural reproductions—artificial teeth—can be produced from ceramic materials and/or acrylic materials. With these materials especially the translucency and/or transparency of the enamel of the original natural teeth can be well approximated.
The task of replacing a tooth is conventionally made of two separate steps. The first step is to measure the shape and color shade of a tooth to be replaced and the second step is to make a duplicate of that tooth according tot he measurements taken in the first step. In the first step, while the shape information can be acquired with molding technique, the measurement of the color shade and translucency of the tooth proves to be more challenging. The quality of the dental prosthesis cannot be better than the data that serves to model the original tooth. The precision of that model depends on several factors, like the quality of the illumination, the data acquisition by measuring and the processing of those data. The oldest and simplest way of determining the color shade of an object like a tooth is to compare visually the object with a chart of color shades. The results obtained with that method are however not very good because of the subjectivity of the human eye.
Furthermore, the illumination of the tooth and of the chart may cause inappropriate color shade choices. A quantitative method can be used to obtain a minimum of precision and of reproductability in the measurement of the color shade of an object. Such quantitative methods can be classified by the type of illumination used, the measurement technique, the data processing and the comparison between the finished product and the original object.
Another measurement technique is taught by Murljacic in his U.S. Pat. No. 5,766,006 issued on Jun. 16, 1998. In this document, Murljacic describes a tooth shade analyzer system using a camera to capture a digital color image of a tooth. The tooth image includes an RGB chromaticity representation that is scanned and compared pixel by pixel with several tooth shades stored in a memory of the system.
A drawback of Murljacic's system is that the scanning is performed without controlling the illumination therefore decreasing the reproductability of the color comparison. Several methods are known and used to convert the spectral decomposition or the data collected from a selected area into a single measurement that corresponds to the color perception of the human eye. The objective is to quantize the data and also to correct them as to be able to recreate the proper colors of the original model as the human eye perceives them. It is also important to be able to quantize the translucency of the materials.
In PCT WO. 97/01308 an oral camera connected to a shade analyzer subsystem, e.g. a digital video processor, and a color display monitor. The camera captures a digital color image of the patient's tooth and the subsystem compares that image to a stored plurality of tooth shades. Each tooth shade is represented in a block of data, including color image data, a toothshade digital word, and a manufacturer type. The patient's tooth image includes an RBG chromatically representation that is scanned and compared with the several tooth shades stored in memory, and a match is determined and communicated to a user of the system. The methodology includes the specification of fractional tooth shades, if needed, corresponding to a plurality of porcelain firms for manufacturing a reconstructed tooth.
The information is then used by a technician to layer the crown following the identified color shade as measured and presented by the digital device. This process of fabricating a crown by a way of layering the material by hand is fairly tedious and costly as it takes much hands-on time. The result of this hand-work is unpredictable especially the shape and dimensions and the result depends in a great deal on the skills of the dental technician.
In EP-0796596 a system for recording the form and shade structure of teeth is described. The system is applied in the preparation and the production of ceramic or acrylic veneered restorations. The system consists of different assortments containing the models and images as well as layering schemes of different tooth form and shade structures. At the patient a comparison is made between the form and shade of the patients' teeth with the models, whereby the best fitting assortment is selected and in the dental laboratory according to the accompanying layering schemes nature-like restorations can be reproduced.
Although the use of a computer is mentioned as an optional component of the assortment, all 2D-representations are directed to production of restorations in the dental laboratory. Because the restorations are layered without a volumetric control especially form, shape and dimensions of the finished artificial tooth of a computer aided manufacturing system subjective uncertainty remains in the final restoration.
In U.S. Pat. No. 5,759,030 a color measuring system and method such as for determining the color or other characteristics of teeth are described. Perimeter receiver fiber optics are spaced apart from a central source fiber optic and receive light reflected from the surface of the tooth being measured. The system utilizes the perimeter receiver fiber optics to determine information regarding the height and angle of the probe with respect to the tooth being measured. Under processor control, color measurement may be made at a predetermined height and angle. Translucency, fluorescence and/or surface texture data also may be obtained. The data generated by the system may be used to implement an automated material mixing machine for the material of which the prosthesis is made. Color and other data taken from a measurement may be used to determine or predict quantities of pigment or other materials for the recipe. Dental prostheses may be layered to simulate the degree of translucency of the tooth.
It is possible to measure for example four measurements for four regions of the tooth and send to the computer, with the data for the four color measurements (such as RBG or other values) associated with the four regions in accordance to the entered parameters.
Another advanced computer assisted system has become known as the Shade Scan System (Cortex Machina, Montreal, Quebec, Canada). It consists of an intraoral camera probe with specially designed optics that allows a spectral measurement of color and translucency. Instead of one or more local measurements on the tooth, as is done with the previous systems, the Shade Scan System includes a complete and global representation of the tooth's properties. The software consists of a shade selection process that translates the optical data into a simple and precise schematic color fields over the whole tooth. The color fields are identified and represented by numbers from an assortment of porcelain of a particular brand. The color fields can be selected as a fine discrimating sensitivity or a more coarser division of color fields. The software allows a representation of translucent areas with a dark-light shade mapping of the whole tooth. This makes the vertical height of the optically more dense areas of the tooth (“mamelons”) visible.
Because results of the digital color analyzer only result in prosthesis through the manual labor of the dental technician, the pseudo trial and error methods are used in the manufacturing of the prosthesis remain, with the result that prosthesis needs to be remade, leading to increased costs and inconvenience to the patient, dental professional and dental laboratory.